Clinical Thyroidology® for the Public

Summaries for the Public from recent articles in Clinical Thyroidology
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THYROID AND PREGNANCY
Is thyroid autoimmunity still a risk factor in women undergoing fertility treatment?

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BACKGROUND
Thyroid autoimmunity, or autoimmune thyroid disease, includes a group of disorders that are caused by antibodies that get confused and attack the thyroid. These antibodies are the most common cause of both hyperthyroidism (Graves’ disease) and hypothyroidism (Hashimoto’s thyroiditis). The antibodies can also be present in individuals with normal thyroid function. Thyroid autoimmunity has for many years been considered associated with a poor outcome in women undergoing fertility treatment. As with spontaneous pregnancies, thyroid autoimmunity was associated with a higher pregnancy loss rate and lower live birth rate. However, many initial studies were done in women who were being treated for autoimmune thyroid disease, namely hypothyroidism. Recent studies now question this association in women who have normal thyroid function.

This study investigated the association of thyroid autoimmunity with fertility treatment and live birth rates in a group of infertile women with normal thyroid function and positive thyroid antibodies.

THE FULL ARTICLE TITLE
 Rao M et al 2022 Thyroid autoimmunity is not associated with embryo quality or pregnancy outcomes in euthyroid women undergoing assisted reproductive technology in China. Thyroid. Epub 2022 Dec 26. PMID: 36571280.

SUMMARY OF THE STUDY
This was a study of couples undergoing fertility treatment (either in vitro fertilization or intracytoplasmic sperm injection) in a hospital setting in China between 2016 and 2022. All included women had concentrations of serum thyroid function tests within the laboratory reference range prior to treatment. Thyroid autoimmunity was defined as elevated serum thyroid peroxidase antibodies (TPOAbs) or thyroglobulin antibodies (TgAbs).

The study included 3444 cycles from 2945 women without thyroid autoimmunity and 499 women with thyroid autoimmunity. Thyroid autoimmunity-positive women were significantly older (average age 31.6 vs. 30.9) and had a higher TSH at baseline (average 2.40 vs. 2.21 mIU/L) than thyroid autoimmunity-negative women. The proportions of thyroid autoimmunity positivity was 13.6% in women <35 years of age and 17.3% in those ≥35. There were no significant differences between women with and those without thyroid autoimmunity in any of the many investigated outcomes. The main effect on outcomes was the age of the mother and was similar in women with and those without thyroid autoimmunity: age <35 years 10% early loss rate vs 22.5% early loss rate in those >35 years and live birth rates 63.9% in women <35 years vs 37.1% in those >35 years.

WHAT ARE THE IMPLICATIONS OF THIS STUDY?
This study shows that thyroid autoimmunity had no effect on pregnancy outcomes after fertility treatment as long as the mother has normal thyroid function. There was a significant difference in outcomes based on age, but this was unaffected by thyroid autoimmunity. This is welcome information for women that have positive thyroid antibodies but normal thyroid function that are undergoing fertility treatment.

— Alan P. Farwell, MD

ABBREVIATIONS & DEFINITIONS

Autoimmune thyroid disease: a group of disorders that are caused by antibodies that get confused and attack the thyroid. These antibodies can either turn on the thyroid (Graves’ disease, hyperthyroidism) or turn it off (Hashimoto’s thyroiditis, hypothyroidism).

In-vitro or intracytoplasmic sperm injection fertilization: a procedure when an egg is fertilized outside of the body and then implanted in a woman to achieve a pregnancy

TPO antibodies: these are antibodies that attack the thyroid instead of bacteria and viruses, they are a marker for autoimmune thyroid disease, which is the main underlying cause for hypothyroidism and hyperthyroidism in the United States.

Thyroglobulin antibodies: these are antibodies that attack the thyroid instead of bacteria and viruses, they are a marker for autoimmune thyroid disease, which is the main underlying cause for hypothyroidism and hyperthyroidism in the United States.

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